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Wetmore, Alexander, 1886-, et al. / Warm-blooded vertebrates
(1931)

Chapter III: color and its arrangement,   pp. 25-38 PDF (5.6 MB)


Page 26


BIRDS
the fat underlying the skin of the cardinal and scarlet
tanager is tinged a deep orange, in contrast to the yellow
fat of sparrows and warblers which do not possess a red
pigment. This zooerythrin in birds resembles in structure
the red pigment of crabs and lobsters, and seems to de-
pend for its formation upon certain elements in the food
of the species concerned. Flamingos and scarlet ibises
kept in captivity often fade in color with successive molts
until they are bleached almost to white, but if fed on
shrimp when the feathers are being renewed they may
retain their brilliance of plumage.
Yellow pigment, known as zooxanthin, is allied to the
red but has a somewhat different chemical composition.
It is seen to good advantage in the yellow species of orioles
and the yellow-headed blackbird. The head color in the
latter, when the new feathers are first grown, is deep
orange, darker in some individuals than in others; but
after the feathers mature the orange color bleaches to a
light yellow or in some individuals almost to white.
The dark pigments or melanins occur in small particles
which are permanently fixed and cannot be dissolved by
chemicals. This characteristic distinguishes them from
the fatty pigments, which may be dissolved by treatment
with alcohol, ether, chloroform, or other chemical reagents,
depending upon their form. The size of the pigment
granules in the melanin series has much to do with the
shade of color produced. For example, it has been found
that in the tumbler pigeon, a variety of the domestic
pigeon, one and the same pigment may produce a black,
brown, slate, or silver hue, according to the form, size, and
abundance of the pigment granules.
Leaving the pigments of birds to consider what are
known as their structural colors we find ourselves in a
world of sham and pretense, as the colors apparent to the
eye are found on analysis to be quite different from what
they seem. For the greater part, they have as a basis some
relatively dull pigment with an overlying layer of feather
(261


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